Process for purifying impure diphenols

ABSTRACT

A process for improving the quality of diphenols by recrystallization from aqueous solvent systems.

This invention relates to a process for purifying impure diphenols whichcomprises recrystallizing the impure diphenol from water in the presenceof polar, aprotic co-solvents.

BACKGROUND OF THE INVENTION

It is well known that the purity of diphenols is of paramount importanceregarding the quality of polymers which are prepared therefrom. Isomericdiphenols that often accompany the p,p'-diphenols are often deleterioussince they do not participate as well in polymerization processes. It isthus desirable and important to obtain the p,p'-diphenols in theirhighest purity in order to secure the quality of the polymers which areprepared therefrom. Since isomeric diphenols always accompany thedesired p,p'-diphenols, purification of the impure reaction products isalways necessary.

In the past, purification of impure mixtures of p,p'-diphenols was mostoften affected by the use of organic solvents such as benzene, methylenechloride or toluene. The use of these and similar solvents results incostly purification due to both the cost of solvents and inefficiency ofthe method. Another purification method is set forth in U.S. Pat. No.3,919,330. This method involves dissolving crude2,2-bis(4-hydroxyphenyl)propane in ethylene glycol and then adding acertain amount of water whereby the 2,2-bis(4-hydroxyphenyl)propane isprecipitated and is then recovered. However, this method requires theuse of large amounts of ethylene glycol and the necessity of anadditional step of separating the water from the aqueous mother liquorin order to recover and reuse the anhydrous glycol.

DESCRIPTION OF THE INVENTION

It has been discovered that p,p'-diphenols of high purity can beobtained by recrystallizing the impure p,p'-diphenol from water, in thepresence of polar, aprotic co-solvents. One method to achieve thisrecrystallization comprises dispersing the impure p,p'-diphenol inwater, heating the resulting slurry and then adding a water solublepolar, aprotic co-solvent until the dissolution or near dissolution ofthe diphenol results, at or near the boiling point of water or thesolvent system. Subsequent cooling and recovery of the solids yieldsp,p'-diphenols of improved quality (assay).

Alternatively, the impure diphenols are heated with a premixed water andpolar, aprotic co-solvent mixture, with stirring, until dissolution ornear dissolution results, followed by cooling and subsequent recovery ofthe solid purified p,p'-diphenol.

The water soluble polar, aprotic co-solvents are those which neitheryield a proton to the solute, nor gain one from it. Water soluble polar,aprotic co-solvents effective herein include amides, sulfoxides,sulfones, phosphoramides, sulfamides, nitriles, ethers and the like.Examples of these water soluble polar, aprotic co-solvents includedimethylformamide, dimethylacetamide, dimethylsulfoxide,dimethylsulfone, tetrahydrothiophene-1,1-dioxide,hexamethylphosphoramide, sulfamide, tetramethylsulfamide,tetramethylurea, dioxane, tetrahydrofuran, N-methylpyrrolidene,acetonitrile, etc. and mixtures thereof. Also, these water solublepolar, aprotic co-solvents may be used with the water soluble alcoholicor phenolic co-solvent, as described in co-pending application A, ofVictor Mark and Charles Vernon Hedges Ser. No. 755,982, filed on thesame date as the instant application and assigned to the same assigneeas the present application, and/or with the watersoluble organiccarboxylic acid, as described in co-pending application B, of VictorMark and Charles Vernon Hedges Ser. No. 755,983 filed on the same dateas the instant application and assigned to the same assignee as thepresent application. Applications A and B are incorporated herein byreference. Also, one or more of these polar, aprotic co-solvents andwater may be employed simultaneously to accomplish recrystallization.

The amount of water soluble polar, aprotic co-solvent employed herein isdependent upon the amount of water used in the recrystallization, inthat the higher the amount of water per solute, the greater the amountof co-solvent that will be required.

A wide variety of diphenols may be purified according to the method ofthe instant invention. These diphenols include 4,4'-thiodiphenol,4,4'-oxydiphenol, cyclohexylidenediphenol, p,p'-biphenol,2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane, as well as thecorresponding tetrachloro and tetrabromo analogs, p,p'-sulfonyldiphenol,bis(3,5-dimethyl-4-hydroxyphenyl sulfone), and2,2-bis(4-hydroxyphenyl)propane. In particular, the impure2,2-bis(4-hydroxyphenyl)propane consists of a mixture of the p,p' ando,p' isomers and, depending on the method of preparation, of a host ofother impurities. Some of these isomers are more soluble than the p,p'isomer and some are less so. It is, therefore, convenient to add to theaqueous slurry of the impure reaction mixtures just enough co-solventthat is necessary for the dissolution of the o,p' and p,p' isomercontent of the mixture, leaving the lesser soluble componentsundissolved. The latter are conveniently removed by filtration.Subsequent cooling of the filtered solution deposits the less solublep,p' isomer, leaving much or all of the more soluble o,p' isomer andother more soluble components in solution. Further cooling, preferablybelow ambient temperature of separation of the solvent mixture bydistillation, often under reduced pressure, separates out or leavesbehind the more soluble impurities.

The maximum temperature of the instant purification method is notcritical, although sometimes it is determined by the boiling point ofthe lowest boiling co-solvent. When working at atmospheric pressure, itis desirable to stay near about 90° to 100° C. so that the solventproperties of water can be best utilized. Since the solubility ofdiphenols increases dramatically with temperature, it is oftenadvantageous to use superatmospheric pressure, such as those obtained bypressurizing the recrystallization vessels by inert gases or byemploying autogeneous pressures. In some cases, 150° C. or even highertemperatures are preferable, such as those available by the use ofsuperheated steam.

It was found that the use of aqueous solvents results usually in theformation of well developed larger crystals, which can be readilyseparated by filtration. In the case of 2,2-bis(4-hydroxyphenyl)propane,the crystals have the rhombic crystal structure which may have on theirsurfaces a contamination of the more soluble isomeric impurities,usually the o,p' isomer. A simple slurrying or rinsing of these crystalsby a proper solvent, such as methylene chloride, readily removes theimpurities and leaves behind the crystals of the pure p,p' isomers.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The following examples are set forth to illustrate more clearly theprinciple and practice of this invention to those skilled in the art.Unless otherwise specified, where parts or percents are mentioned, theyare parts or percents by weight.

EXAMPLE I

To a one liter three necked flask, equipped with a stirrer, refluxcondenser, addition funnel and thermometer, there was charged 50 gramsof 2,2-bis(4-hydroxyphenyl)propane (bisphenol-A) and 500 ml. of waterand the resultant slurry was heated with the aid of a heating mantel.When the water started to reflux, pure dimethylformamide was graduallyadded to the aqueous heterogeneous liquid until a clear solutionresulted. It required 135.2 grams of the co-solvent formamide to yield aclear solution. Upon cooling to ambient temperature, with continuousstirring, well developed rhomboid crystals of p,p'-biphenol-A separatedout, that were isolated by filtration in nearly quantitative yield.

EXAMPLES II to VI

The procedure of Example I was repeated exactly, except thatdimethylformamide was replaced with the co-solvents and in the amountsshown in Table I.

                  TABLE I                                                         ______________________________________                                        Co-solvents Required to Dissolve 50 Grams                                     of Bisphenol-A in 500 gms. of Water at 100° C.                         Example                                                                              Co-solvent     Amount of Co-solvent (gms.)                             ______________________________________                                        II     Acetonitrile   152.3                                                   III    Tetramethylurea                                                                              259.4                                                   IV     Dioxane        229.0                                                   V      Dimethylsulfoxide                                                                            155.1                                                   VI     Tetrahydrothiophene-                                                                         183.2                                                          1,1-dioxide                                                            ______________________________________                                    

Obviously, other modifications and variations of the present inventionare possible in the light of the above teachings. It is therefore to beunderstood that changes may be made in the particular embodiments of theinvention described which are within the full intended scope of theinvention as defined by the appended claims.

What is claimed is:
 1. A process for purifying impure p,p' -diphenolswhich comprises dispersing the impure diphenol in water, heating theresulting slurry, adding a water soluble polar, aprotic co-solvent untilthe dissolution or near dissolution of the diphenol slurry results at ornear the boiling point of water or the solvent system, cooling thesolution to achieve the separation of the purified diphenol andrecovering the purified p,p' -diphenol.
 2. A process according to claim1 wherein the polar, aprotic co-solvent is selected from the groupconsisting of amides, sulfoxides, sulfones, phosphoramides, sulfamides,nitriles and ethers.
 3. A process according to claim 2 wherein theco-solvent is selected from the group consisting of dimethylformamide,dimethylsulfoxide, N-methylpyrrolidene and acetonitrile.
 4. A processaccording to claim 1 wherein the impure diphenol is2,2'-bis(4-hydroxyphenyl)propane.
 5. A process according to claim 1wherein the dissolution or near dissolution of the diphenol slurryresults at about 90° to 100° C at atmospheric pressure.
 6. A processaccording to claim 1 wherein the dissolution or near dissolution of thediphenol slurry is carried out at super-amtospheric pressure.
 7. Aprocess for purifying impure p,p' -diphenols which comprises dispersingthe impure diphenol in a mixture of water and a water soluble polar,aprotic co-solvent or mixtures of co-solvents, heating the resultantslurry until the dissolution or near dissolution is achieved, coolingthe solution to achieve the separation of the purified diphenol andrecovering the purified p,p' -diphenol.
 8. A process according to claim7 wherein the polar, aprotic co-solvent is selected from the groupconsisting of amides, sulfoxides, sulfones, phosphoramides, sulfamides,nitriles and ethers.
 9. A process according to claim 8 wherein theco-solvent is selected from the group consisting of dimethylformamide,dimethylsulfoxide, N-methylpyrrolidene and acetonitrile.
 10. A processaccording to claim 7 wherein the impure diphenol is crude2,2'-bis(4-hydroxyphenyl)propane.
 11. A process according to claim 7wherein the dissolution or near dissolution of the diphenol slurryresults at about 90° to 100° C at atmospheric pressure.
 12. A processaccording to claim 7 wherein the dissolution or near dissolution of thediphenol slurry is carried out at super-atmospheric pressure.